The present invention is related to a head driving technique of a liquid jet device, which suppresses drive currents of piezoelectric elements provided in correspondence with nozzles used to jet liquid droplets in a jetting head of a liquid jet device, such as an ink-jet type printer.
Currently, while ink-jet type color printers In which several colors of ink droplets are jetted from recording heads have been popularized as output apparatus of computers, these ink-jet type color printers have been widely employed In order to print images processed by computers and the like in multicolor and multi-gradation modes.
For instance, in an ink-jet type printer using piezoelectric elements as driving elements for jetting ink, since a plurality of piezoelectric elements which are provided in correspondence with a plurality of nozzles of a print head are selectively driven, ink droplets are jetted from the nozzles based upon dynamic pressure of the respective piezoelectric elements, and the ink droplets are attached to print paper, so that dots are formed on this print paper so as to perform a printing operation.
In this case, the respective piezoelectric elements are provided in correspondence with nozzles used to jet the ink droplets therefrom, and are driven by drive signals which are supplied from a driver IC (head driving circuit) mounted within the print head so as to jet the ink droplets.
Such a head driving apparatus is arranged as shown in, for example, FIG. 10. In FIG. 10, a head driving apparatus 10 includes piezoelectric elements 11, a head driving circuit 12, a current amplifying circuit 13, and a nozzle selecting switch circuit 14. The piezoelectric elements 11 are provided in correspondence with a plurality of nozzles of an ink-jet printer. The head driving circuit 12 is employed so as to supply a drive signal with respect to one electrode 11a of each of these piezoelectric elements 11. The current amplifying circuit 13 and the nozzle selecting switch circuit 14 are provided between the head driving circuit 12 and each of the piezoelectric elements 11.
Each of the piezoelectric element 11 is constructed in such a manner that this piezoelectric element 11 is displaced in response to a voltage applied between both the electrodes 11a and 11b. The head driving circuit 12 is employed In order to generate a drive signal xe2x80x9cCOMxe2x80x9d for driving the print head of the ink-jet printer, and is arranged, for example, within a main body of the ink-jet printer.
The current amplifying circuit 13 is constructed of two transistors 13a and 13b. Within these transistors 13a and 13b, a collector of the first transistor 13a is connected to a constant voltage source, a base thereof is connected to one output of the head driving circuit 12, and an emitter thereof is connected to an input side of the nozzle selecting switch circuit 14. As a result, this first transistor 13a becomes conductive in response to a signal supplied from the head driving circuit 12, and thus, supplies a drive waveform having a trapezoidal shape via the nozzle selecting switch circuit 14 to the piezoelectric elements 11.
Also, an emitter of the second transistor 13b is connected to an input side of the nozzle selecting switch circuit 14, a base thereof is connected to a second output of the head driving circuit 12, and a collector thereof is connected to the ground. As a result, the second transistor 13b becomes conductive in response to a signal supplied from the head driving circuit 12, and thus, discharges the piezoelectric elements 11 via the nozzle selecting switch circuit 14.
The nozzle selecting switch circuit 14 is turned ON at drive timing of the corresponding piezoelectric element 11 by inputting thereinto a control signal, and then, outputs the drive signal COM to the piezoelectric element 11. In an actual case, this nozzle selecting switch circuit 14 is arranged as a so-called xe2x80x9ctransmission gate (TG)xe2x80x9d in order to turn ON/OFF the respective piezoelectric elements 11. In this case, in the head driving apparatus 10 having such an arrangement, the current amplifying circuit 13 may drive all of the piezoelectric elements 11 connected by one set of these transistors 13a and 13b. 
As a consequence, since a transistor having such a maximum current capable of supplying a current required when all of the piezoelectric elements 11 are driven at the same time is needed as these transistors 13a and 13b, the transistors used in the current amplifying circuit 13 are relatively high cost, so that the cost of the resulting head driving apparatus 10, and thus, the cost of an ink-jet type printer using this head driving apparatus 10 are increased. Also, when the large currents flow through the transistors, waveforms thereof are easily distorted.
Furthermore, in some cases, for instance, plural stages of transistors such as Darlington-connected transistors must be employed so as to supply a large current, so that the cost thereof would be increased and the characteristic thereof would be deteriorated.
On the other hand, in the head driving apparatus 10, there is a rare case that all of the piezoelectric elements 11 are simultaneously driven during the normal printing operation. In general, a half, or a smaller number of the entire piezoelectric elements 11 are driven at the same time. More specifically, this trend may become conspicuous in such a case that multiple color ink is used in a color printer. For example, in the case of a six-colored ink printer, ⅓, or smaller number of piezoelectric elements are driven at the same time in an average condition. If more than ⅓ of piezoelectric elements are driven at the same time, print paper is excessively wet, so that better printing operation cannot be carried out. To the contrary, there is a very small possibility that all of ink nozzles are locally jetted. In other words, if all of ink nozzles are jetted and thereafter a time period is provided during which all of ink nozzles are not jetted, then all of ink nozzles may be locally jetted in, for example, a six-color ink printer, even when the entire nozzle number is averaged to become approximately ⅓ of the total ink nozzle number.
As a consequence, such a head driving apparatus has been proposed in, for example JP-A-6-115116 and JP-A-1-178456. In this head driving apparatus, when print data is entered by which a predetermined number, or larger numbers of loads are simultaneously driven, since a total number of such loads which are driven at the same time is limited, a transistor having a smaller maximum current is used.
In the head driving apparatus of JP-A-6-115116, the method for processing the print data by the MPU so as to limit the total ON-number of the nozzle selecting switch circuit has been proposed.
Also, in the head driving apparatus of JP-A-1-178455, such a method has been proposed. That is, while the output current of the current amplifying circuit is monitored, when this output current is increased higher than the predetermined value, the total ON-number of the nozzle selecting switch circuit is limited.
However, the above-described methods own the below-mentioned problems. That is, in the case of JP-A-6-115116, since the print data is sequentially processed by the MPU, the data processing speed is restricted, so that the printing speed would be suppressed. Otherwise, since the highspeed-operable MPU must be employed, the cost of the head driving apparatus is increased.
Also, in the case of JP-A-1-178455, when the output current supplied from the power supply actually becomes larger than, or equal to a predetermined current value, a total number of piezoelectric elements which are subsequently driven is restricted. This method has a major object capable of protecting the power supply. Even when a large current having a pulse shape instantaneously flows from the power supply, if the subsequently-driven load is light, then there is no problem as to this power supply. On the other hand, in such a case that this method has an object capable of protecting the transistor, an actual drive current never exceeds a prelimited current even in an instantaneous time instant. However, even when actually flowing currents are monitored, there is a certain possibility that an actual drive current may instantaneously exceed the normal value as to the maximum current of the transistor used in the current amplifying circuit. Under certain condition, the transistor is damaged, or is brought into a break down state.
It is therefore an object of the present invention to provide a head driving apparatus having a simple arrangement of a liquid jet device, capable of amplifying drive current signals, while an amplifying element having a relatively smaller maximum current is employed.
In order to achieve the above object, according to the present invention, to solve the above-described problem, in a head driving apparatus of the present invention, a total number of nozzles which should be simultaneously driven is calculated based upon a control signal supplied to a switch circuit, and when the calculated total nozzle number exceeds a preselected number, only a portion of entire piezoelectric elements corresponding to the nozzles is driven so as to perform a printing operation.
That is to say, a head driving apparatus comprising:
a plurality of nozzles;
a switch circuit, having a plurality of switch units corresponding to the nozzles, and selecting the nozzles from which a liquid droplet is jetted at predetermined jet timing;
a head driving circuit, supplying a drive signal to the switch circuit to jet the droplet from the nozzles;
a controller, supplying a control signal to the switch circuit so as to ON-OFF control the switch units every jet timing based upon jetting data; and
a restriction signal generator, generating a restriction signal,
wherein a part of the switch units are turned OFF in spite of the control signal supplied to the switch circuit when the switch circuit receives the restriction signal.
Preferably, the restriction signal generator calculates a total number of the switch units to be turn ON simultaneously in accordance with the control signal, and supplies a restriction signal to the switch circuit when the total number exceeds a predetermined number.
In the above configurations, the determination unit calculates a total number of the switch units which must be turned ON, namely, a total quantity of the piezoelectric elements to which the drive signals must be applied at the same time based upon the control signal every jet timing In such a case that this calculated quantity does not exceed a predetermined number, the determination unit does not output the restriction signal with respect to the switch circuit.
As a consequence, the switch circuit ON/OFF-controls the switch units corresponding to the respective piezoelectric elements based upon the control signal supplied from the printer main body, and thus, selectively applies the drive signals amplified by the current amplifying circuit to the respective piezoelectric elements, so that the printing operation may be carried out.
In this case, if the total number of the switch units to be simultaneously turned ON which has been calculated every jet timing exceeds the predetermined number, namely if the total quantity of the piezoelectic elements to which the drive signals must be simultaneously applied exceeds the predetermined number, then the determination unit outputs the restriction signal with respect to the switch circuit.
Then, the switch circuit turns OFF a part of the switch units irrespective of the control signal supplied from the printer main body, and also, ON/OFF-controls only other switch units corresponding to the respective piezoelectric elements based upon the control signal supplied from the printer main body, so that the switch circuit may selectively apply the drive signals amplified by the current amplifying circuit to the respective piezoelectric elements.
As a result, since the partial switch units are turned OFF, the piezoelectric elements corresponding to these partial switch units are not driven, so that the printing operation is not carried out. As a consequence, since the total number of piezoelectric elements which are turned ON at the same time is limited, the output current of the current amplifying circuit for amplifying the drive signal is limited lower than, or equal to a predetermined value. Accordingly, while the maximum current of the amplifying element employed In the current amplifying circuit may be selected to be the small maximum current, the cost thereof may be reduced, and also, such an arrangement of multiple stages is no longer required, and further, the characteristic thereof may be improved.
Also, after all of the data every jet timing have been finished to be transferred, the judging operation is carried out by the determination unit, so that the judging operation may be quickly carried out, the highspeed printing operation may be properly carried out, and also, the judging operation may be performed before the printing operation is actually carried out. As a result, there is no possibility that the current larger than, or equal to a predetermined current value may flow.
Preferably, the predetermined number is a half number of the entire switch units, and the switch circuit turns OFF a half number of the entire switch units when the switch circuit receives the restriction signal.
In the above configuration, upon receipt of the restriction signal from the determination unit, the nozzle selecting circuit turns OFF a half number of the entire switch units irrespective of the control signal derived from the main body of the liquid Jetting apparatus, and also, ON/OFF-controls only a remaining half number of the switch units corresponding to the respective piezoelectric elements based upon the control signal supplied from the main body of the liquid jetting apparatus, so that the drive signals amplified by the current amplifying circuit are selectively applied to the respective piezoelectric elements.
As a consequence, since the half number of the above-explained switch units are turned OFF, a total number of piezoelectric elements which are driven at the same time is limited to a half number of the entire piezoelectric elements, so that the output current of the current amplifying unit for amplifying the drive signals can be limited smaller than, or equal to a predetermined value. Accordingly, while the maximum current of the amplifying element of the current amplifying circuit may be made small, the cost thereof can be reduced, the arrangement having the multiple stage is no longer required, and thus, the characteristic thereof can be improved.
Preferably, a first jetting operation is performed while the switch circuit brings a part of the switch units into OFF state based upon the restriction signal, and a second jetting operation is performed on the same path while the switch circuit brings the part of the switch units into ON state and another part of the switch units into OFF state after the first jetting operation is performed.
In the above configuration, when the total number of the switch units to be simultaneously turned ON, which has been calculated every jet timing, namely, the number of the piezoelectric elements to which the drive signals should be applied, exceeds a predetermined number, and then, the determination unit outputs the restriction signal with respect to the switch circuit, the switch circuit sequentially uses all of the switch units every plural sets of these switch units to perform the printing operations respectively. As a result, while a total number of the piezoelectric elements which are simultaneously driven is limited, the entire printing operation can be firmly carried out.
Here, it is preferable that, a first jetting operation is performed while the switch circuit brings a half number of the entire switch units into OFF state based upon the restriction signal, and a second jetting operation is performed on the same path while the switch circuit brings the half of the switch units into ON state and a remained part of the switch units into OFF state after the first jetting operation is performed.
In the above configuration, when the total number of the switch units to be simultaneously turned ON, which has been calculated every Jet timing, namely, the number of the piezoelectric elements to which the drive signals should be applied, exceeds a predetermined number, and then, the determination unit outputs the restriction signal with respect to the switch circuit, the switch circuit sequentially uses all of the switch units every a half set of the entire switch units to perform the printing operations respectively. As a result, while a total number of the piezoelectric elements which are simultaneously driven is limited, the entire printing operation can be firmly carried out.
Furthermore, in this case, the output current of the current amplifying circuit may be reduced to a half value thereof, and the entire printing operation may be completely carried out by executing the printing operation two times.
Preferably, the restriction signal generator calculates a simultaneous drivable number of piezoelectric elements applying pressure to liquid so as to jet a liquid droplet from the nozzles, based upon a maximum inclination of a waveform of the drive signal, a capacitance of the piezoelectric element per a single nozzle, and an allowable current of an amplifier circuit which amplifies the drive signal, and stores the calculated result as the predetermined number.
In the above configuration, for instance, even when the jetting mode is switched, or the capacitances of the piezoelectric elements are changed due to temperature changes, since the simultaneous drivable number of the optimum piezoelectric elements is stored as the predetermined number, the output current of the current amplifying circuit during the printing operation can be firmly restricted to become smaller than, or equal to the maximum current of the amplifying element which constitutes the current amplifying circuit.
According to the present invention, there is also provided a nozzle selecting IC, comprising;
a selector, selecting a jetting nozzle from a plurality of nozzles based upon jetting data; and
a restrictor, restricting a specific nozzle of the nozzles to a non-jetting state in response to a restriction signal supplied from an external in spite of the jetting data.
In the above configuration, since the specific nozzle can be set to the non-jetting nozzle by receiving the restriction signal irrespective of the print data, a total quantity of such piezoelectric elements which are simultaneously driven can be limited, so that the output current of the current amplifying circuit for amplifying the drive signal may be limited to become smaller than, or equal to the predetermined value. As a consequence, while the maximum current of the amplifying element of the current amplifying circuit may be selected to be a small maximum current, the cost thereof may be reduced, and such an arrangement of multiple stages is no longer required, and further, the characteristic thereof may be improved.
According to the present invention, there is also provided a method for driving a head driving apparatus, comprising the steps of:
providing a plurality of nozzles;
supplying a drive signal for jetting the liquid droplet from the nozzles;
supplying a control for controlling a jet of the liquid droplet based upon jetting data every jet timing;
selecting the nozzles from which the liquid droplet is jetted in accordance with the control signal at predetermined jet timing; and
restricting a part of the nozzle into a non jetting state in spite of the control signal.
Preferably, the method further comprises a step of calculating a total number of the nozzles from which the liquid droplet is jetted simultaneously in accordance with the control signal, and the part of the nozzle is restricted into a non jetting state in spite of the control signal when the total number exceeds a predetermined number.
Preferably, a half number of the entire nozzles are restricted into the non jetting state when the total number exceeds a predetermined number.
Preferably, the method further comprising:
performing a first jetting operation while a part of the nozzles are restricted into non jetting state; and
performing a second jetting operation on the same path while the part of the nozzles are jetting state and another part of the nozzles are non jetting state.
Here, it is preferable that, the method further comprising:
performing a first jetting operation while the half number of the entire nozzles are restricted into non jetting state; and
performing a second jetting operation on the same path while the half of the entire nozzles are jetting state and the remained part of the nozzles are non jetting state.
According to the present invention, there is also provided a head driving apparatus, comprising:
a plurality of nozzles from which a liquid droplet is jetted;
a data storing unit storing jetting data for jetting the liquid droplet on a one path in a movement of a jetting head having the nozzles, the jetting data having a first part and a second part; and
a divider, dividing the jetting data,
wherein the liquid droplet is jetted in accordance with a first part of the jetting data in a jetting operation of the one path;
wherein the divider divides the second part of the jetting data Into a plurality of divided data; and
wherein the liquid droplet is jetted in a plurality of jetting operations in accordance with the plurality of divided data respectively after the jetting operation is finished.
Preferably, the head driving apparatus further comprises an identifier which adds identification information to the second part of the jetting data.
Preferably, the liquid droplet is jetted in accordance with the jetting data added with the identification information.
Preferably, the first part and the second part of the jetting data are defined during the liquid droplet is jetted in accordance with the jetting data.
According to the present invention, there is also provided a method for driving a head driving apparatus, comprising the steps of:
providing a plurality of nozzles from which a liquid droplet is jetted;
providing a data storing unit;
providing a divider;
storing a jetting data in the data storing unit, the data having a first part and a second part;
jetting the liquid droplet in accordance with a first part of the jetting data in a jetting operation of a one path;
dividing the second part of the jetting data into a plurality of divided data;
jetting the liquid droplet in accordance with the divided data after the jetting operation is finished; and
repeating the jetting step of the divided data until the liquid droplet is jetted in accordance with all divided data.
Preferably, the method further comprises the step of adding identification information to the second part of the jetting data
Preferably, the liquid droplet is jetted In accordance with the jetting data added with the identification information.
Preferably, the first part and the second part of the jetting data are defined during the liquid droplet is jetted in accordance with the jetting data.